Change docker-compose YAML files to use PostgreSQL version 12 image for "postgres" and "hybrid" types of database setup

docker/docker-compose.hybrid.yml

@@ -19,7 +19,7 @@ version: '2.2'
 services:
   postgres:
     restart: always
-    image: "postgres:11.6"
+    image: "postgres:12"
     ports:
       - "5432"
     environment:

docker/docker-compose.postgres.yml

@@ -19,7 +19,7 @@ version: '2.2'
 services:
   postgres:
     restart: always
-    image: "postgres:11.6"
+    image: "postgres:12"
     ports:
     - "5432"
     environment: